In the product_manufacturer_id column, you get the id of the manufacturer.
Variants are added as extra lines: one line for the main product, one line for each of its variants.
If you want to have the name instead of the id of the manufacturer, you will have to edit the file "export" of the view "product" of your back end template via the menu Display>Views. There change:
echo '"'.str_replace('"','""',$product->$column).'"'.$separator;
to:
if($column == 'product_manufacturer_id'){
$categoryClass = hikashop_get('class.category');
$category = $categoryClass->get($product->$column);
echo '"'.str_replace('"','""',$category->category_name).'"'.$separator;
}else{
echo '"'.str_replace('"','""',$product->$column).'"'.$separator;
}